packet: nlmon: virtual netlink monitoring device for packet sockets
Currently, there is no good possibility to debug netlink traffic that
is being exchanged between kernel and user space. Therefore, this patch
implements a netlink virtual device, so that netlink messages will be
made visible to PF_PACKET sockets. Once there was an approach with a
similar idea [1], but it got forgotten somehow.
I think it makes most sense to accept the "overhead" of an extra netlink
net device over implementing the same functionality from PF_PACKET
sockets once again into netlink sockets. We have BPF filters that can
already be easily applied which even have netlink extensions, we have
RX_RING zero-copy between kernel- and user space that can be reused,
and much more features. So instead of re-implementing all of this, we
simply pass the skb to a given PF_PACKET socket for further analysis.
Another nice benefit that comes from that is that no code needs to be
changed in user space packet analyzers (maybe adding a dissector, but
not more), thus out of the box, we can already capture pcap files of
netlink traffic to debug/troubleshoot netlink problems.
Also thanks goes to Thomas Graf, Flavio Leitner, Jesper Dangaard Brouer.
[1] http://marc.info/?l=linux-netdev&m=113813401516110
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/nlmon.c b/drivers/net/nlmon.c
new file mode 100644
index 0000000..dc364be
--- /dev/null
+++ b/drivers/net/nlmon.c
@@ -0,0 +1,170 @@
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/netdevice.h>
+#include <linux/netlink.h>
+#include <net/net_namespace.h>
+#include <linux/if_arp.h>
+
+struct pcpu_lstats {
+ u64 packets;
+ u64 bytes;
+ struct u64_stats_sync syncp;
+};
+
+static netdev_tx_t nlmon_xmit(struct sk_buff *skb, struct net_device *dev)
+{
+ int len = skb->len;
+ struct pcpu_lstats *stats = this_cpu_ptr(dev->lstats);
+
+ u64_stats_update_begin(&stats->syncp);
+ stats->bytes += len;
+ stats->packets++;
+ u64_stats_update_end(&stats->syncp);
+
+ dev_kfree_skb(skb);
+
+ return NETDEV_TX_OK;
+}
+
+static int nlmon_is_valid_mtu(int new_mtu)
+{
+ return new_mtu >= sizeof(struct nlmsghdr) && new_mtu <= INT_MAX;
+}
+
+static int nlmon_change_mtu(struct net_device *dev, int new_mtu)
+{
+ if (!nlmon_is_valid_mtu(new_mtu))
+ return -EINVAL;
+
+ dev->mtu = new_mtu;
+ return 0;
+}
+
+static int nlmon_dev_init(struct net_device *dev)
+{
+ dev->lstats = alloc_percpu(struct pcpu_lstats);
+
+ return dev->lstats == NULL ? -ENOMEM : 0;
+}
+
+static void nlmon_dev_uninit(struct net_device *dev)
+{
+ free_percpu(dev->lstats);
+}
+
+static struct netlink_tap nlmon_tap;
+
+static int nlmon_open(struct net_device *dev)
+{
+ return netlink_add_tap(&nlmon_tap);
+}
+
+static int nlmon_close(struct net_device *dev)
+{
+ return netlink_remove_tap(&nlmon_tap);
+}
+
+static struct rtnl_link_stats64 *
+nlmon_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
+{
+ int i;
+ u64 bytes = 0, packets = 0;
+
+ for_each_possible_cpu(i) {
+ const struct pcpu_lstats *nl_stats;
+ u64 tbytes, tpackets;
+ unsigned int start;
+
+ nl_stats = per_cpu_ptr(dev->lstats, i);
+
+ do {
+ start = u64_stats_fetch_begin_bh(&nl_stats->syncp);
+ tbytes = nl_stats->bytes;
+ tpackets = nl_stats->packets;
+ } while (u64_stats_fetch_retry_bh(&nl_stats->syncp, start));
+
+ packets += tpackets;
+ bytes += tbytes;
+ }
+
+ stats->rx_packets = packets;
+ stats->tx_packets = 0;
+
+ stats->rx_bytes = bytes;
+ stats->tx_bytes = 0;
+
+ return stats;
+}
+
+static u32 always_on(struct net_device *dev)
+{
+ return 1;
+}
+
+static const struct ethtool_ops nlmon_ethtool_ops = {
+ .get_link = always_on,
+};
+
+static const struct net_device_ops nlmon_ops = {
+ .ndo_init = nlmon_dev_init,
+ .ndo_uninit = nlmon_dev_uninit,
+ .ndo_open = nlmon_open,
+ .ndo_stop = nlmon_close,
+ .ndo_start_xmit = nlmon_xmit,
+ .ndo_get_stats64 = nlmon_get_stats64,
+ .ndo_change_mtu = nlmon_change_mtu,
+};
+
+static struct netlink_tap nlmon_tap __read_mostly = {
+ .module = THIS_MODULE,
+};
+
+static void nlmon_setup(struct net_device *dev)
+{
+ dev->type = ARPHRD_NETLINK;
+ dev->tx_queue_len = 0;
+
+ dev->netdev_ops = &nlmon_ops;
+ dev->ethtool_ops = &nlmon_ethtool_ops;
+ dev->destructor = free_netdev;
+
+ dev->features = NETIF_F_FRAGLIST | NETIF_F_HIGHDMA;
+ dev->flags = IFF_NOARP;
+
+ /* That's rather a softlimit here, which, of course,
+ * can be altered. Not a real MTU, but what is to be
+ * expected in most cases.
+ */
+ dev->mtu = NLMSG_GOODSIZE;
+}
+
+static __init int nlmon_register(void)
+{
+ int err;
+ struct net_device *nldev;
+
+ nldev = nlmon_tap.dev = alloc_netdev(0, "netlink", nlmon_setup);
+ if (unlikely(nldev == NULL))
+ return -ENOMEM;
+
+ err = register_netdev(nldev);
+ if (unlikely(err))
+ free_netdev(nldev);
+
+ return err;
+}
+
+static __exit void nlmon_unregister(void)
+{
+ struct net_device *nldev = nlmon_tap.dev;
+
+ unregister_netdev(nldev);
+}
+
+module_init(nlmon_register);
+module_exit(nlmon_unregister);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Daniel Borkmann <dborkman@redhat.com>");
+MODULE_AUTHOR("Mathieu Geli <geli@enseirb.fr>");
+MODULE_DESCRIPTION("Netlink monitoring device");